Patent CA-1075443-A (CA)
Inventor: HENDERSON JAMES M
IPC: B01D53/34
Filed: 1976-03-09
Granted: 1980-04-15
Abstract: ABSTRACT OF THE DISCLOSURE         Ammonia is added to aqueous scrubbing solution contain-ing an organic base-sulfurous acid reaction product, preferably an aromatic amine-sulfurous acid reaction product, an organic base-sulfuric acid reaction product, preferably an aromatic amine-sulfuric acid reaction product and water in a separating zone located exteriorly of an absorption tower.  The aqueous scrubbing solution is obtained from a sulfurous acid solution scrubbing sec-tion of the absorption tower wherein an organic base, preferably an aromatic amine, is utilized as absorbent in a lower absorber section of the tower to remove SO2 from a SO2-containing gas mix-ture, followed by scrubbing the SO2-depleted, aromatic amine-en-riched effluent gas from the absorber section with sulfurous acid-and ammonium sulfate-containing aqueous solution in the upper sulfurous acid scrubbing section of the tower to remove sub-stantially all of the gaseous aromatic amine from the gas.  The sulfur dioxide-impoverished, substantially organic base absorbent-free effluent gas from the sulfurous acid scrubbing zone is dis-charged from this scrubbing zone and ultimately to the atmosphere without any additional scrubbing of this effluent gas, after its discharge from such scrubbing zone, with sulfuric acid solution or any other acid solution or any acid.  The sulfur dioxide is strip-ped from the pregnant aromatic amine absorbent from the absorbing section in the stripping section of a stripping tower.  The am-monia treatment of the aqueous scrubbing solution in the external separating zone results in release of the aromatic amine from the aromatic amine-sulfuric acid reaction product present therein by reaction of the ammonia with the aromatic amine-sulfuric acid reaction product and also in the formation of ammonium sulfate.          An aqueous liquid solution containing the ammonium sulfate and the aromatic amine-sulfurous acid reaction product separates as a lower layer from the released aromatic amine present in an upper layer in the separating zone and this aqueous liquid solution is with-drawn from the lower layer thereof in the separating zone and passed to the regenerator section of a stripping tower.  Aromatic amine and SO2 gas are liberated in the regenerator section and a considerable quantity of steam is generated therein.  Aqueous solution containing ammonium sulfate is withdrawn from the lower portion of the regenerator section and, after bleeding off only a small portion of this aqueous solution, is passed, after cooling, into the upper portion of the sulfurous acid scrubbing section of the absorption tower and introduced therein.  SO2 gas, obtained in the process, is supplied into the lower portion of this sulfur-ous acid scrubbing section and is dissolved in water of the intro-duced aqueous ammonium sulfate solution to form sulfurous acid.          The use of ammonia for treating the aqueous scrubbing solution in the separating Zone to release organic base, preferably aromatic amine and form ammonium sulfate enables the passage of the major portion of the aqueous ammonium sulfate-containing liquid solution withdrawn from the regenerator to the sulfurous acid scrubbing zone while requiring the bleed off of only a small amount, at most, of the potentially polluting aqueous ammonium sulfate-con-taining liquid solution prior to its introduction into the sulfur-ous acid scrubbing zone.  Further, the presence of ammonium sulfate during the dissolution of the SO2 gas in the water in the sulfurous acid scrubbing section enhances the dissolution of the SO2 in the water.  Moreover the removal of gaseous organic base from the SO2-impoverished gas by scrubbing with sulfurous acid produced from part of the SO2 obtained in the process results in eliminating the requirement to purchase considerable. quantities of sulfuric acid to provide the relatively large quantities of dilute sulfuric acid required by prior art processes for the re-moval of SO2 from gas mixtures and hence eliminates the consider-able monetary expense of purchasing the sulfuric acid.